1. Field of the Invention
The present invention relates to a method for producing L-amino acids generated via a biosynthetic pathway in which pyruvic acid is an intermediate during fermentation of coryneform bacteria. The L-amino acids which can be generated via this method are L-glutamic acid, L-arginine, L-glutamine, L-proline, L-valine, L-alanine, and L-lysine.
2. Brief Description of the Related Art
An L-amino acid such as L-glutamic acid is generated via a biosynthetic pathway in which pyruvic acid is an intermediate. L-amino acids are conventionally produced on an industrial scale by fermentative methods utilizing coryneform bacteria, including Brevibacterium and Corynebacterium. To improve the L-amino acid-productivity of coryneform bacteria, strains isolated from nature or artificial mutants thereof have been used. (JP07-121228B, JP07-121228B, JP06-237779A, Adv Biochem Eng Biotechnol. 2003; 79:59-112. J. Biotechnol. 2003 Sep. 4; 104(1-3):155-72. and WO95/34672)
When aerobic bacteria, especially coryneform bacteria, are cultured under oxygen-limited conditions, organic acids other than the target substance, such as lacetic acid and acetic acid, accumulate in excess amounts as byproducts. Such accumulation inhibits the growth of the bacteria and greatly reduces their productivity during fermentation. Furthermore, excess amounts of counter ions which neutralize such organic acids are necessary, which increases the production cost. Accordingly, creating strains that produce less acetic acid during culture is desirable, such as strains in which the activity of an enzyme that catalyzes production of acetic acid is reduced or eliminated.
Examples of fermentation methods using a strain in which the activity of an enzyme that catalyzes production of acetic acid is reduced or eliminated include producing L-amino acids using Escherichia coli which is deficient in the activities of phosphoacetyltransferase (pta) and lactate dehydrogenase (ldh) (WO99/06532), producing L-amino acids using Enterobacteriaceae family which is deficient in the activity of pyruvate oxidase (poxB), and producing D-panthotheic acid using Enterobacteriaceae which is deficient in the activity of pyruvate oxidase (poxB) (WO02/36797).
Acetate kinase (ack) and phosphotransacetylase (pta) have been reported as enzymes that are involved in the assimilation of acetic acid in coryneform bacteria (Microbiology, 1999 February; 145(Pt2):503-13). Also, a coryneform bacterium in which the acetate-producing enzyme pyruvate oxidase (poxB) is disrupted has been reported (EP1096013A).
Acetyl-CoA hydrolase (3.1.2.1) produces acetic acid from acetyl-CoA and H2O, and the nucleotide sequence predicted to encode acetyl-coA hydrolase of Corynebacterium glutamicum has been disclosed (EP1108790A). However, there has been no report on the actual cloning and expression analysis of the gene; and thus the actual function of the gene has not been confirmed yet.